The toxic compounds called cyanides threaten our health and environment. Harmful to man, and even more so to aquatic life, these compounds are produced and introduced into our environment in many damaging ways, so that it is important to understand and restrict this form of environmental pollution. Measuring the cyanides in a selected sample is one important step in the process of improving the environment.
Of the various existing types and kinds of analytical methology and related apparatus employed to measure cyanides, automated systems have achieved notable results. For example, refer to U.S. Pat. No. 4,265,857, and to a publication entitled "Chemistry of Wastewater Technology" published by Ann Arbor Science Publishers, Inc. of Ann Arbor Michigan, Library of Congress Catalog Card No. 76-50991, ISBN 0 250 40185-1, which are incorporated herein by reference.
As described in Chapter 20 of "Chemistry of Wastewater Technology," such an automated system involves the steps of separation, absorption, and measurement, with ultraviolet irradiation being employed to dissociate cyanides in the process of separation, along with thin-film distillation and chemical absorption techniques.
A typical ultraviolet radiation unit includes an ultraviolet lamp, surrounded by a quartz coil, through which is passed an acidic sample to be tested. The quartz coil passes all of the several energy levels, or spectral lines, of ultraviolet radiation produced by the ultraviolet lamp, of wave lengths between approximately 150 millimicrons and 400 millimicrons. This spectrum of ultraviolet radiation causes the break down of all cyanide complexes, including the strong iron and cobalt cyanide complexes. The cobalt complex is dissociated by the ultraviolet radiation both of approximately 255 millimicrons, and of approximately 310 millimicrons. In this manner, the cyanides are dissociated for subsequent measurement.
The thin-film distillation separates the resulting hydrogen cyanide gas, and the HCN gas is then absorbed in a sodium hydroxide solution for subsequent colorimetric measuring. Thus, all of the cyanides can be detected and measured in a large number of different samples in a continuous, automated manner.
The quartz coil in the conventional irradiation unit of the system is permeable to all, or at least substantially all, of the ultraviolet spectrum, thereby enabling the ultraviolet radiation to break down all of the cyanide complexes in the acidic sample. However, thiocyanate (SCN) is also dissociated, and therefore, is detected along with the cyanides, thereby causing somewhat inaccurate higher cyanide measurements. Thus, dissociation of the thiocyanate is unwanted and undesirable for most applications. Consequently, while the present cyanide detection measurement system is satisfactory for most applications, it would be highly desirable to have a cyanide measurement system, which would dissociate all the cyanide complexes, including the strong cobalt complex, without dissociating thiocyanate.